The specific objectives for the total period of requested support are: 1) to define the active site on insulin 2) to locate the site or sites of insulin binding in tissues 3) to define the intermolecular interactions between insulin and tissue receptors and 4) to study the mechanisms by which insulin causes its various actions. We feel that in order to accomplish these objectives that the most reliable initial approach is to define the intramolecular and intermolecular interactions of insulin that are related to the biological activity or activities of insulin. We feel this way because the precise structure of insulin is now known and we are convinced that these parameters are at the present time the most valid available criteria that will yield information valuable in accomplishing the major objectives of this proposal. The approaches to be employed in arriving at the objectives of this project can best be divided into three areas: 1) Studies concerned with the effect of Zn on insulin structure, antigenicity and action 2) Studies concerned with insulin binding on degradation by mouse liver plasma membranes and 3) Studies concerned with localization of insulin in tissues. It should be emphasized that these areas are interrelated. The subdivisions are arbitrary, being employed only to clarify the overall approach to obtain our objectives.